Association Constants Of Complexes Research Articles

Study on the interactions between RS-licarbazepine and carboxyethylated cyclodextrins by electrokinetic chromatography and nuclear magnetic resonance

The interactions taking place in the enantiomeric separation of the antiepileptic drug licarbazepine by Electrokinetic Chromatography (EKC) using two carboxyethylated cyclodextrins (CE-CDs) (CE-β-CD and CE-γ-CD) as chiral selectors were investigated in this work to intend to explain the reversal in the enantiomer migration order observed depending on the CD. As these CDs were mixtures of isomers, only apparent and estimated association constants for enantiomer-CD complexes could be calculated based on EKC experiments, which agreed with the enantiomer migration order observed for CE-β-CD but not for CE-γ-CD. Additional experiments were carried out using NMR to study the stoichiometry of the complexes formed, their association constants and their structure. The construction of the corresponding Job plots, from 1H NMR titrations and intermolecular NOE interactions (between some of licarbazepine’s aromatic protons and the internal hydrogens of both CDs), permitted to conclude in the formation of 1:1 inclusion complex in both cases. Also, Scott plots for both systems were obtained showing a linear behavior for CE-β-CD while a non-linear behavior was observed for CE-γ-CD. As a result, only the apparent association constant for licarbazepine-CE-β-CD complexes was calculated (0.309 mM−1) (no significant differences between licarbazepine enantiomers were found in all NMR experiments). The structure of the complexes originated by licarbazepine and both CE-CDs was investigated. Insertion complexes were formed in each case, although some structural differences were noticed as the licarbazepine-CE-γ-CD complex would be less tight than that with CE-β-CD. Molecular dynamics (MD) simulations corroborated the structures derived from NMR results.

ESIPT-based fluorescent enhanced probes prompted by methylated β-cyclodextrin for the detection of thiophenols

Thiophenol and its derivatives are compounds with high toxicity to organisms and environmental pollution, so it is necessary to detect the level of thiophenols in the environment and biological samples. The probes 1a-b were obtained by introducing the 2,4-dinitrophenyl ether group into diethylcoumarin–salicylaldehyde based compounds. And they can form host-guest compounds with methylated β-cyclodextrin (M-β-CD), the association constants of inclusion complexes are 49.2 M−1, 125 M−1 respectively. The fluorescence intensities of probes 1a-b at 600 nm (1a) and 670 nm (1b) increased significantly in thiophenols detection. Meanwhile, with the addition of M-β-CD, the hydrophobic cavity of M-β-CD significantly increased the fluorescence intensity of probes 1a-b, thus the detection limits of probes 1a-b to thiophenols were reduced from 410 nM, 365 nM to 62 nM, 33 nM respectively. Whereas, the good selectivity and short response time of probes 1a-b towards thiophenols was not affected in the presence of M-β-CD. Moreover, probes 1a-b were used for further water sample detection and HeLa cell imaging experiments due to their good response to thiophenols and the results suggested that probes 1a-b had the potential to detect the content of thiophenols in water samples and living cells.

Complexation between the Antioxidant Pterostilbene and Derivatized Cyclodextrins in the Solid State and in Aqueous Solution.

Inadequate aqueous solubilities of bioactive compounds hinder their ability to be developed for medicinal applications. The potent antioxidant pterostilbene (PTB) is a case in point. The aim of this study was to use a series of modified water-soluble cyclodextrins (CDs), namely, hydroxypropyl β-CD (HPβCD), dimethylated β-CD (DIMEB), randomly methylated β-CD (RAMEB), and sulfobutyl ether β-CD sodium salt (SBECD) to prepare inclusion complexes of PTB via various solid, semi-solid, and solution-based treatments. Putative CD-PTB products generated by solid-state co-grinding, kneading, irradiation with microwaves, and the evaporative treatment of CD-PTB solutions were considered to have potential for future applications. Primary analytical methods for examining CD-PTB products included differential scanning calorimetry and Fourier transform infrared spectroscopy to detect the occurrence of binary complex formation. Phase solubility analysis was used to probe CD-PTB complexation in an aqueous solution. Complexation was evident in both the solid-state and in solution. Complex association constants (K1:1) in an aqueous solution spanned the approximate range of 15,000 to 55,000 M-1; the values increased with the CDs in the order HPβCD < DIMEB < RAMEB < SBECD. Significant PTB solubility enhancement factors were recorded at 100 mM CD concentrations, the most accurately determined values being in the range 700-fold to 1250-fold.

Exploring Interaction Dynamics of Designed Organic Charge Transfer Complex of 6-Aminoindole and Chloranilic Acid: Spectrophotometric, Characterization, Computational, Antimicrobial, and DNA Binding Properties

The chemistry of a new charge and proton transfer hydrogen bonded complex (PT CT) between the donor 6-Aminoindole (6 AMI) and the π-acceptor Chloranilic acid (CLA) has been explored in acetonitrile (ACN), methanol (MeOH), and 50% acetonitrile + 50% methanol (ACN-MeOH) at 25 °C by using electronic absorption spectroscopy. By exploiting Job's and the photometric titration methods, the molar proportion of the PT CT complex was confirmed as 1:1. The modified Benesi-Hildebrand principle was used to evaluate the association constant (KCT) and molar absorptivity (ƐCT) of the PT CT complex, and these values indicate that the produced PT CT complex is more stable. In three different solvents, the effect of solvent polarity on charge transfer spectra was also observed. Different spectroscopic physical parameters were assessed in different polar solvents, including energy (ECT), ionization potential (ID), resonance energy (RN), oscillator strength (f), dissociation energy (W), standard gibbs free energy (ΔGo), transition dipole movement (μEN), and these were also within the accepted values, confirming the stability of the formed PT CT complex. The produced solid PT CT complex was analyzed by using FT-IR, NMR, TGA-DTA, and SEM-EDX spectra. Powder XRD analysis was used to determine the PT CT complex nature and crystalline size. The biological activity of the current PT CT complex has been screened in antimicrobial and DNA binding studies. The synthesized PT CT complex was shown to have excellent antimicrobial activity and DNA binding affinity. Therefore, in the future, it may be used as a pharmaceutical drug for bacterial and fungal infections. The computational studies were carried out by using DFT analysis, and the functions were used to B3LYP and CAM B3LYP in the gas phase, with the basis set being 6-31G + (d, p). The bond lengths, bond angles, Mulliken atomic charges, MEP maps, reactivity parameters, and FMO surfaces were also calculated. The computational analysis is additionally supported by the experimental studies of the PT CT complex.

Enhancement of association constants of various charge-transfer complexes in siloxane solvents

The association constants of various charge-transfer complexes were evaluated in n-hexane, octamethyltrisiloxane and PDMS to investigate the solvent effect.

Adjusting the Structure of β-Cyclodextrin to Improve Complexation of Anthraquinone-Derived Drugs.

β-Cyclodextrin (CD) derivatives containing an aromatic triazole ring were studied as potential carriers of the following drugs containing an anthraquinone moiety: anthraquinone-2-sulfonic acid (AQ2S); anthraquinone-2-carboxylic acid (AQ2CA); and a common anthracycline, daunorubicin (DNR). UV-Vis and voltammetry measurements were carried out to determine the solubilities and association constants of the complexes formed, and the results revealed the unique properties of the chosen CDs as effective pH-dependent drug complexing agents. The association constants of the drug complexes with the CDs containing a triazole and lipoic acid (βCDLip) or galactosamine (βCDGAL), were significantly larger than that of the native βCD. The AQ2CA and AQ2S drugs were poorly soluble, and their solubilities increased as a result of complex formation with βCDLip and βCDGAL ligands. AQ2CA and AQ2S are negatively charged at pH 7.4. Therefore, they were less prone to form an inclusion complex with the hydrophobic CD cavity than at pH 3 (characteristic of gastric juices) when protonated. The βCDTriazole and βCDGAL ligands were found to form weaker inclusion complexes with the positively charged drug DNR at an acidic pH (pH 5.5) than in a neutral medium (pH 7.4) in which the drug dissociates to its neutral, uncharged form. This pH dependence is favorable for antitumor applications.

Azocalix[4]arene-Rhodamine Supramolecular Hypoxia-Sensitive Systems: A Search for the Best Calixarene Hosts and Rhodamine Guests.

A potential hypoxia-sensitive system host-guest complex of three calixarenes (including two with four anionic carboxyl and sulphonate azo fragments on the upper rim and a newly synthesized bis-azo adduct of calixarene in the cone configuration with azo fragments on the lower rim with the most widespread cationic and zwitterionic rhodamine dyes (123, 6G and B)) was studied using UV-VIS spectrometry and fluorescence as well as 1D and 2D NMR techniques. It was found that all three calixarenes form a complex with rhodamine dyes with a 1:1 composition. The association constants of calixarene-dye complexes with sulfonate calixarenes, especially in the case of tetra-anionic calixarene, turned out to be higher compared with carboxyl calixarene due to the more intense electrostatic interactions. For the first time using an HRESI MS technique, it was shown that the treatment of rhodamine 6G and 123 with sodium dithionite (SDT) produces a non-fluorescent leuco form of the dye, and only rhodamine B can be used with SDT without the occurrence of a side reduction. Moreover, it was identified that in addition to the reduction in the azo groups, SDT causes partial cleavage of the aryl ether bonds. The found features of SDT should be taken into account when SDT is used as an azoreductase mimic.

Evaluation of the Direct Interaction between Amino Acids and Glutathione-Coated CdTe Quantum Dots and Application in Urinalysis for Histidine Determination

The present work aimed to direct amino acid (AA) sensing by quantum dots (QD) and development of an analytical method for potential fast clinical tests. Notably, AA with a positive charge or neutral polar chains, namely L-histidine (His) and L-threonine (Thr), responded to glutathione-coated CdTe (GSH-CdTe) (ΔF ≤ 90%, variation of fluorescence intensity). However, in ammoniacal buffer (0.25 mol L-1) at pH 8.0, 2.2 nm GSH-CdTe responded only to His. Static quenching with complex association constant (Ksv) varying from 2.81 to 0.94 (10 L mol-1) as well as van der Waals forces and/or hydrogen bonding were predicted for His-QD quenching mechanism and binding type. Additionally, thermodynamic parameters as ΔH = -76.5 kJ mol-1 (enthalpy), ΔS = -227.4 J K-1 mol-1 (entropy) and ΔG from -9.8 until -6.4 kJ mol-1 (Gibbs free energy) at 20 to 35 °C were estimated by van’t Hoff equation. Under optimal conditions, the developed method presented a linear range from 0.42 to 35 mmol L-1 (with correlation coefficient (r) of 0.9970, n = 7), good precision (relative standard deviations (RSD) < 2.5% for 2.5 and 20 mmol L-1; n = 6) and limit of detection 1.6 × 10-4 mol L-1 (0.025 mg mL-1). Recovery tests were performed on artificial urine and human urine samples with recoveries ranging from 78.7 to 127.6%.

Recognition of hydrophilic molecules in deep cavitand hosts with water-mediated hydrogen bonds.

We describe new container host molecules - deep cavitands with benzimidazole walls and ionic feet - to recognize highly hydrophilic guest molecules in water. The aromatic surfaces of the cavity recognize hydrophobic portions of the guest while bound water molecules mediate hydrogen bonding in the complex. Spectroscopic (NMR) evidence indicates slow in/out exchange on the chemical shift timescale and thermodynamic (ITC) methods show large association constants (Ka up to 6 × 104 M-1) for complexation of small, water-soluble molecules such as THF and dioxane. Quantum chemical calculations are employed to optimize the host-guest geometries and elucidate the hydrogen bonding patterns responsible for the binding.

Supramolecular Assemblies Constructed from Cucurbit[8]uril and N‐Alkyl Carboxymethylbenzotriazole through Host‐Guest Interactions

AbstractDifferent supramolecular self‐assembly between 1‐dodecyl‐3‐carboxymethylbenzotriazole (Lc12), 1‐octyl‐3‐carboxymethylbenzotriazole (Lc8) and 1‐butyl‐3‐carboxymethylbenzotriazole (Lc4) in the solid state and in aqueous solution has been investigated. For Lc12@CB[8] system, 1 : 1 host‐guest complexes were formed in aqueous solution and 2 : 2 host‐guest complexes were formed in the solid state, and the dodecyl chains adopted contorted conformations when bound to CB[8] molecules. For Lc8@CB[8] system, 1 : 1 host‐guest complexes were formed both in aqueous solution and in solid state, and the alkyl chain and benzotriazole moiety of guest Lc8 were both squeezed into the cavity of the CB[8]. The Lc4@CB[8] system was similar to Lc8@CB[8], 1 : 1 host‐guest complexes were formed in aqueous solution, the alkyl chain and benzotriazole moiety of guest Lc4 were encapsulated into the cavity of the CB[8]. Isothermal titrations in water afforded high apparent association constants for complexes Lc12@CB[8], Lc8@CB[8]and Lc4@CB[8].

Doxorubicin exhibits strong and selective association with VEGF Pu22 G-quadruplex

BackgroundVascular endothelial growth factor (VEGF), is upregulated in tumor cells and thus became a potential therapeutic target for anti-cancer drugs. Recent reports suggested the use of Doxorubicin (Dox) with VEGF-targeting siRNAs for an enhanced decrease in VEGF expression. Besides, VEGF-B gene therapy was found to suppress the cardiotoxicity effects of Dox. On the other hand, even though Dox is a commonly used anti-cancer agent, its mechanism of actions isn't completely mapped out. Herein, the interactions between a G4 structure formed by the VEGF promoter region Pu22 and Dox were investigated. MethodsThe Dox-G4 interactions were examined via competition dialysis, UV–vis Absorption, Circular Dichroism (CD) and Fluorescence spectroscopy. ResultsThe results demonstrated that Dox was stabilizing the VEGF Pu22 G4 structure and the calculated association constant for VEGF Pu22-G4 complex (Ka = 7.50 × 106) was very close to the reported Ka values for Dox-dsDNA complexes. Additionally, the competition dialysis experiments revealed the selectivity of Dox to Pu22 compared to other G4 structures formed in telomeric repeats and promoter regions such as BCL-2 and C-myc. ConclusionsDox exhibits strong and selective association with VEGF Pu22 G4 structure that was comparable to its well-known association with dsDNA. General significanceThe results presented here might be useful in the general area of antitumor drug-DNA interactions. Doxorubicin's significant affinity to VEGF Pu22 G4 might be one of the plausible mechanisms behind its anti-tumor activity.

Chromatographic study of four sesquiterpenoids in volatile oil of Curcumae Rhizoma on reverse phase stationary phase with methyl-β-cyclodextrin as mobile additive

The elution behavior of four sesquiterpenoids in volatile oil of Curcumae Rhizoma on reverse-phase high-performance liquid chromatography with methyl-β-cyclodextrin as mobile phase additive was studied, including germacrone, curzerene, furanodiene, and β-elemene. Stoichiometric ratio and apparent formation constants of inclusion complex formed by methyl-β-cyclodextrin and each analyte were calculated by varying the concentration of the additive in the mobile phase composed of methanol and water (90:10, v/v), in which the association constant for inclusion complex formed by the organic modifier methanol and methyl-β-cyclodextrin was also determined. Results showed that the stoichiometric ratio of all the inclusion complex was 1:1 when 0–9 mmol L−1 of methyl-β-cyclodextrin was added in the mobile phase. Unusual retention behavior of the analyte germacrone was found, which was further investigated by the calculation of thermodynamic parameters. Meanwhile, enthalpy and entropy of the inclusion complexes and solute-stationary phase interactions were determined by linear van’t Hoff plots.

Quenching of [Ce(H2O)n]3+ Fluorescence by Graphene Oxide

Static fluorescence quenching by graphene oxide at various concentrations was observed by measuring the relative fluorescence intensity and excited-state lifetime of optically excited Ce3+ ions in aqueous cerium nitrate solutions. The measured Stern–Volmer association constant of Ce aqua complexes with graphene oxide was 24.7 L/g, which was significantly less than the constants for cationic rhodamine dyes and metal cations and was explained by the negative charges on the interacting species.

Benchmarking of Halogen Bond Strength in Solution with Nickel Fluorides: Bromine versus Iodine and Perfluoroaryl versus Perfluoroalkyl Donors.

The energetics of halogen bond formation in solution have been investigated for a series of nickel fluoride halogen bond acceptors; trans‐[NiF(2‐C5NF4)(PEt3)2] (A1), trans‐[NiF{2‐C5NF3(4‐H)}(PEt3)2] (A2), trans‐[NiF{2‐C5NF3(4‐NMe2)}(PEt3)2] (A3) and trans‐[NiF{2‐C5NF2H(4‐CF3)}(PCy3)2] (A4) with neutral organic halogen bond donors, iodopentafluorobenzene (D1), 1‐iodononafluorobutane (D2) and bromopentafluorobenzene (D3), in order to establish the significance of changes from perfluoroaryl to perfluoroalkyl donors and from iodine to bromine donors. 19F NMR titration experiments have been employed to obtain the association constants, enthalpy, and entropy for the halogen bond formed between these donor‐acceptor partners in protiotoluene. For A2–A4, association constants of the halogen bonds formed with iodoperfluoroalkane (D2) are consistently larger than those obtained for analogous complexes with the iodoperfluoroarene (D1). For complexes formed with A2–A4, the strength of the halogen bond is significantly lowered upon modification of the halogen donor atom from I (in D1) to Br (in D3) (for D1: 5≤K 285≤12 m −1, for D3: 1.0≤K 193≤1.6 m −1). The presence of the electron donating NMe2 substituent on the pyridyl ring of acceptor A3 led to an increase in −ΔH, and the association constants of the halogen bond complexes formed with D1–D3, compared to those formed by A1, A2 and A4 with the same donors.

Hydrogen bonding between ethynyl aromates and triethylamine: IR spectroscopic and computational study.

Ethynylpyridines (EPs) and ethynylbenzene (EB) are multifunctional systems able to participate in hydrogen-bonded complexes as both donors and acceptors of the H-atom. Their structures and stabilities are mainly a function of the hydrogen-bonding properties of the partner in the complex and the surroundings in which the complexation occurs. In this paper, IR spectroscopy and quantum chemical calculations are employed to characterize hydrogen-bonded complexes of 2- and 3-EP and EB with triethylamine (TEA) in tetrachloroethene (C2Cl4) solution. The formation of CH⋯N hydrogen bonds is experimentally confirmed by the appearance of TEA concentration-dependent signals in the IR spectra of the EPs and EB. Along with the signals due to unassociated CH and CC oscillators (2-EP: 3308 cm-1 and 2120 cm-1; 3-EP: 3308 cm-1 and 2116 cm-1; EB: 3313 cm-1 and 2113 cm-1) weak, red-shifted signals arise at ~3215 ± 5 cm-1 and ~2105 ± 5 cm-1 which are assigned to the stretching vibrations of hydrogen-bonded CH⋯ and CC⋯ oscillators, respectively. This result is at variance with those of previous investigations of EB and TEA in the gas phase. In the 2-EP⋯TEA complex these bands remain at the same position with increasing TEA concentration. However, in the 3-EP⋯TEA and EB⋯TEA complexes the CH⋯ stretching band demonstrates a slightly reduced red-shift as the TEA concentration increases, whereas the CC⋯ stretching band absorbs at the same wavenumber in the investigated TEA concentration range. The results of B3LYP-D3 calculations indicate that complexes with more or less linear CH⋯N intermolecular hydrogen bonds are more stable than other, dispersion-driven complexes. Complexes with the Cs symmetrical TEA conformer are predicted to have larger binding energy than those formed with the C3 and C1 symmetrical conformers. The predicted IR spectral shifts are slightly different for complexes with the three different TEA conformers. Association constants of hydrogen-bonded complexes at 26 °C are estimated to be ~0.1 mol-1 dm3.

Complex of a new racemic thiourea substrate: Spectrophotometric study and separation of atropisomers

The activity of a chiral molecule can vary from one atropisomer to the other. In this study, the separation of racemic-N-(2-methylphenyl), N’-(2-chlorophenyl) thiourea (H 2 L 2 ), a hydrophobic heavy metal trap, has been studied using reversed-phase high-performance liquid chromatography (RP-HPLC) with hydroxypropyl-beta-cyclodextrin (HP-β-CD) as a complexing additive to the racemic mixture and hexane-isopropanol as a mobile phase. The stoichiometry and the overall association constant of the complex have been determined using the continuous variation (Job's plot) method and the Scott's method respectively.

Quantitative structure -retention relationship modeling of selected antipsychotics and their impurities in green liquid chromatography using cyclodextrin mobile phases.

Applying green chromatography methods is currently one of the challenges in liquid chromatography. Among different strategies, using cyclodextrin (CD) mobile phase modifiers was applied in this paper. CDs can form inclusion complexes with a wide variety of hydrophobic organic compounds and, consequently, affect their retention behavior. CD-containing mobile phases possess complicated complexation and adsorption equilibria so retention is dependent not only on chromatographic parameters and properties of the compound but also on properties of compound-CD complex. Docking study was used to calculate association constants of the selected antipsychotics (risperidone, olanzapine, and their impurities) and β-CD complexes and predict which part of the molecule structure will most likely incorporate into the β-CD cavity. Quantitative structure-retention relationship model (QSRR) for selected model substances was built employing artificial neural network (ANN) technique. Reliable QSRR model was obtained using molecular descriptors, complex association constants, and chromatographic factors. The multilayer perceptron network with 11-8-1 topology, trained with back propagation algorithm, showed the best performance. Root mean square error for training, validation, and test was 0.2954, 0.3633, and 0.4864, respectively. The correlation coefficient (R2) between experimentally obtained retention factor values [k(exp)] and values computed or predicted by ANN [k(ANN)] was 0.9962 for training, 0.9927 for validation, and 0.9829 for test, indicating good predictive ability of the model. The optimized network was used for development of green chromatography method for separation of risperidone and its related impurities, as well as olanzapine and its related impurities in a relatively short run time and with low consumption of organic modifier. The developed methods were validated in accordance with ICH Q2 (R1) quideline and all parameters fulfilled the defined criteria. The greenness of the proposed methods has also been demonstrated. Graphical Abstract Complex association constants as inputs of QSRR model in β-cyclodextrin modified HPLC system and development of green chromatography methods.

Influence of different classes of crosslinkers on alginate polyelectrolyte nanoparticle formation, thermodynamics and characteristics

Complexation of linear alginate polyanions with different classes of crosslinkers (divalent cations, polycations, positively charged surfactants) was investigated, to unravel their effects on nanoparticle formation. The goal was to define the crosslinker-to-alginate molar ratios at which nanoparticles are formed, and to reveal the underlying thermodynamics and molecular interactions using dynamic and electrophoretic light scattering, isothermal titration calorimetry, and infrared spectroscopy. Alginate nanoparticles were formed across a limited range of molar ratios that was specific for each crosslinker, and had different size and stability. Thermodynamic parameters of alginate complexation with crosslinkers showed that nanoparticle formation was in all cases entropy driven, together with a minor enthalpic contribution. The crosslinking mechanism was based on ionic interactions, with accompanying weaker interactions specific for each crosslinker, and involved characteristic macroscopic association constants (Ka1) for complexation of alginate (range, 104–109M−1). Additionally, the ionic strengths of the media influenced the characteristics and stabilities of the polyelectrolyte nanoparticles.

Gold nanoparticles stabilized with βcyclodextrin-2-amino-4-(4-chlorophenyl)thiazole complex: A novel system for drug transport.

While 2-amino-4-(4-chlorophenyl)thiazole (AT) drug and thiazole derivatives have several biological applications, these compounds present some drawbacks, such as low aqueous solubility and instability. A new complex of βCD-AT has been synthesized to increase AT solubility and has been used as a substrate for the deposit of solid-state AuNPs via magnetron sputtering, thus forming the βCD-AT-AuNPs ternary system, which is stable in solution. Complex formation has been confirmed through powder X-ray diffraction and 1D and 2D nuclear magnetic resonance. Importantly, the amine and sulfide groups of AT remained exposed and can interact with the surfaces of the AuNPs. The complex association constant (970 M-1) has been determined using phase solubility analysis. AuNPs formation (32 nm average diameter) has been studied by UV-Visible spectroscopy, transmission/scanning electron microscopy and energy-dispersive X-ray analysis. The in vitro permeability assays show that effective permeability of AT increased using βCD. In contrast, the ternary system did not have the capacity to diffuse through the membrane. Nevertheless, the antibacterial assays have demonstrated that AT is transferred from βCD-AT-AuNPs, being available to exert its antibacterial activity. In conclusion, this novel βCD-AT-AuNPs ternary system is a promising alternative to improve the delivery of AT drugs in therapy.

Synthesis and Anion Binding Assessment of Novel Adamantane Amidopyrroles

Two new adamantane anion receptors with amidopyrrole side arms were prepared and their anion binding ability in DMSO solutions with TBA salts (Cl–, AcO– and H2PO4–) was investigated by UV/Vis spectroscopy. After calculating the corresponding association constants of receptor-anion complexes, it became apparent that only one amidopyrrole side arm was engaged in complexation. These experimental findings were rationalized using computational tools and the binding mode was proposed. In addition to the found 1 : 1 stoichiometry, we showed that the studied receptors bind oxo-anions (H2PO4– and AcO–) more strongly than spherical halogenide (Cl–) anions.